Semiconductor light emitting devices (hereinafter called LED devices unless specifically designated otherwise), fabricated by mounting semiconductor light emitting elements diced from a wafer (hereinafter called LED dies unless specifically designated otherwise) on a leadframe or circuit substrate and packaged by covering them with a material such as a resin or glass, are widely used in various applications. While such LED devices can take various configurations according to the application, LED dies may be mounted on both sides of a leadframe or circuit substrate in order to increase the amount of light emission by enlarging the spreading angle of the LED device while compensating for the strong directional characteristics that the LED dies exhibit.
LED devices with LED dies mounted on both sides of a leadframe have been known for a long time (for example, refer to patent document 1). FIG. 25 is a diagram corresponding to FIG. 2 in patent document 1. For convenience, some of the reference numerals used to designate the component elements have been changed.
In FIG. 25, two light emitting elements (LED dies) 421 are mounted on the left and right sides of a forward end portion of a leadframe 422a. Each light emitting element 421 is electrically connected to a leadframe 422b by a wire. The leadframes 422a and 422b are, respectively, a common positive terminal and a common negative terminal. The light emitting elements 421 are sealed with an epoxy resin 423, and light collecting portions 404 are formed on the left and right sides of the epoxy resin 423. The semiconductor light emitting device shown in FIG. 25 has directional characteristics shown as 404a and 404b in the figure.
When each LED die is connected by a wire, the light emitting efficiency of the LED device decreases because of the shadow of the wire. Furthermore, the size of the LED device increases because there is a need to provide an area for routing the wires. To address this, each LED die having an anode and cathode only on one face thereof (hereinafter called the bottom face) may be connected directly to a leadframe or to electrodes on a circuit substrate (hereinafter called flip-chip mounting). It is known that flip-chip mounting contributes to enhancing the light emitting efficiency and reducing the mounting area. The major reason is that the anode and cathode of the LED die are bonded directly to the leadframe or to the electrodes on the circuit substrate, eliminating the need for the wire.
An LED device with LED dies flip-chip mounted on both sides of a circuit substrate as described above is known in the art (for example, refer to patent document 2). FIG. 26 is a diagram corresponding to FIG. 2 in patent document 2. For convenience, some of the reference numerals used to designate the component elements have been changed.
In FIG. 26, reflective cups 505 for accommodating LED chips 504c are formed substantially centered in the circuit substrate 502 and symmetrically between the upper and lower surface thereof. Each reflective cup 505 includes a bottom face 505a and a sloping face 505b, and electrode patterns 507a and 507b formed on the upper or lower surface of the circuit substrate 502 are disposed opposite each other across a gap formed in the bottom face 505a of the reflective cup 505. The LED chip 504c is flip-chip mounted on the bottom face 505a of the reflective cup 505 in such a manner as to straddle the gap between the electrode patterns 507a and 507b. The reflective cup 505 is filled with an optically transmissive resin 508.
Another possible method for increasing the brightness of the LED device is by increasing the number of LED dies. For example, it is known in the art to mount four or more LED dies on both sides of the circuit substrate (for example, refer to FIG. 1 in patent document 3). FIG. 27 is a diagram corresponding to FIG. 1 in patent document 3. For convenience, some of the reference numerals used to designate the component elements are changed.
FIG. 27 is a cross-sectional view of a light source device (LED device) 605A having a light emitting element (LED die) mounting enamel substrate 601a. In the light source device 605A, light emitting elements 606 are mounted in reflective recessed portions 604d formed in both surfaces J and K of the light emitting element mounting enamel substrate 601a, and the reflective recessed portions 604d are each filled with a transparent resin 609 to seal the light emitting element 606 therein. The light emitting element mounting enamel substrate 601a is formed by covering a core metal 602a with an enamel layer 603, and a total of six reflective recessed portions 604d for accommodating the respective light emitting elements 606 are formed in both surfaces J and K. An electrode 607c for feeding the light emitting elements 606 is formed on top of the enamel layer 603. A portion of the electrode 607c is formed so as to extend into the bottom face of each reflective recessed portion 604d, and the light emitting element 606 is mounted thereon by die bonding or wire bonding.